Functional description

The oil level sensor is attached to the oil sump and is accessible from below. There is no longer an oil dipstick on vehicles with an oil level sensor. These engines have an electronic oil level check. The concept for the display is also new (see Owner's Handbook).

The oil level sensor consists of the evaluation electronics and a measuring tube. There is engine oil in the measuring tube. dependent on the motorization:  In addition, a signal for the engine oil temperature is supplied.

Fig 1: Measuring Tube, Oil-Level Sensor, Three Pin Plug Connection

Courtesy of BMW OF NORTH AMERICA, INC.

The evaluation electronics transmit ultrasonic pulses. These ultrasonic pulses are reflected at the transition point from oil to air (echo impulse). The evaluation electronics receive and amplify these echo impulses. The amplified echo pulses are then converted into a digital signal.

The distance travelled by the sound wave determines the echo lag time. The evaluation electronics calculate the oil level on the basis of the echo lag time. Changes in the engine oil (e.g. ageing or infiltration in the engine oil) and the engine oil temperature influence the signal propagation delay. For this reason compensation is effected in the oil level sensor.

The signals are transmitted to the engine control as pulse-width-modulated signals.